Is GPS navigation really safer?

[Guest airsick]

I was discussing GPS navigation on the weekend and some interesting points came up, one of which is worth a mention here.

 

When we navigate visually most people will drift a little of track, say a mile or two. This is not unsafe and goes uncorrected until you get to your waypoint. At this point you join the circuit and land or do what ever it is you are there to do. When on GPS however it is a different story.

 

Flying by GPS means that you stay dead on track most of the time. Let's say I am flying from point A to point B. Whereas I might stray a little when doing it visually I would remain pretty much spot on if I did the same flight using GPS. Surely this is safer right? Well maybe, maybe not.

 

For ultralights it could be a real concern. In GA we often fly above 5000 ft and stick to the preferred heights. Under 5000 ft this is not necessary so we can do what ever we want (within reason of course). Given that a lot of ultralights are restricted to <5000 ft operations (I am right here aren't I? I still haven't gotten around to my conversion so I am not 100 per cent sure!) they can pretty much always do what they want, again, within reason. This is where the problems arise.

 

Flying from point A to point B at say 4000 ft while another aircraft is flying the reverse track, also at 4000 ft, puts both pilots at risk. Navigatin visually would have meant there would probably be some error in each pilots navigation and they would miss each other (I hope!). Doing it by GPS however significantly increases the chance that they are both on exactly the same route just in opposite directions.

 

The risk of a collision increases on busy routes but also where terrain is involved. If you can fly anywhere between 0 and 5000 ft then there are 10 levels each separated by 500 ft that you may choose. Say the terrain is at 3500 ft then your options become 4000, 4500 and 5000 ft. This assumes that you fly at multiples of 500 ft which I think is a general convention. Thus the risk is increased.

 

It will only get worse when more people begin to use GPS more often as well.

 

Should the preferred levels be enforced to a lower level, say 2000 ft? Or is there some other solution to this potential problem? Is it really a problem? If not will it become one?

 

Interested to hear other peoples views on this.

 

 

[hihosland]

Does not have to be on reciprical headings.

 

Imagine two aircraft one at 60 kts and the other at 110kts flying the same GPS track and the same quadrantal level there is a real risk of the faster aircraft overhauling the slower one. At least with the head on scenario you have two pilots keeping a look and you only need 50% of them to recognise the conflict.

 

With one behind the other only one pilot is in a position to see and avoid and the slow guy is reliant 100% reliant on the faster one's lookout.

 

Davidh

 

 

[markendee]

To be on the exact same track both aircraft would have to have started out from the same place. And both would have had to be flown on the arrow with the same accuracy.

 

Also one tends to ignore the arrow once the airfield is in sight.

 

I can see why you asked the question but probably not a huge worry in my opinion.

 

I do believe a GPS saves fuel by less time wandering off course so that could equate to less incidences due to no fuel. Also maybe less lost aircraft.

 

On the whole more advantages than disadvantages I would think.

 

 

[Guest airsick]

Leaving the arrow with the airfield in sight is a valid point but will only happen in the last few miles.

 

I also agree that aircraft would have to be departing from the same place and have the same destination but still wonder about the problems. I think it is especially pertinent for events such as NatFly.

 

As all of the aircraft begin to converge on the same airport their waypoints may be similar. With the last few waypoints the problem highlighted by Hihosland might become a factor. Imagine the bulk of 700 odd aircraft all approaching Narromine on Friday afternoon using similar waypoints on the last few legs with some travelling at 50kts and others at 150kts. Between midday and 6pm there is only 360 minutes. If half of the aircraft arrive in this timeframe with even spacing that is roughly one per minute. I think there is a fair chance of a problem in these circumstances.

 

I think you are right with respect to the advantages outweighing the disadvantages but does that mean we can ignore this problem? It is certainly something that people should be aware of. (If it is a problem that is.)

 

Perhaps another thing to consider is that people are focussing more and more on the inside of the cockpit with these instruments and looking outside less which just exacerbates the problem even more.

 

 

[facthunter]

Valid point.

 

Airsick, in my opinion, you are on the ball. I have always made it a principle to navigate a little to one side of track, or use tracks that would not be so commonly used. (all other things being equal). The same applies when you are flying a railway line, or a long straight road. The more precise the track-keeping, the greater the chance of collision. Nev...

 

 

[Guest airsick]

Good point Nev. I recall years ago an instructor telling me to do the same thing when following a road, river, railway tracks, etc. I did always wonder though, if everyone is tracking off to the side am I better off flying directly over them? :confused:

 

 

[facthunter]

Still better off.

 

When you introduce a random and variable factor, you increase your chances of missing significantly, even if it is only by 50 ft and you live to tell the tale. Now we can navigate nose to nose very precisely (Bad idea). You're setting it up to happen oneday. Nev...

 

 

[Captain]

This very point was mentioned by Mick Poole in the latest magazine and it is correct, however I would make the following points:

 

 

 

1 In the event that the track overflys part of a CTAF, an overflying radio call would have a good chance of alerting other aircraft who may potentially be in conflict (if they are listening).

 

 

 

2 Why wouldn't all aircraft be flying on the odds & evens +500 ft, up to 5000 ft.

 

 

 

Although it is crazy that if you are flying a course of 0 - 179 degrees, you only have 1500 & 3500 available to you. Many of our aircraft would much prefer 5500 or 7500 and would probably be safer there.

 

 

 

3 To take airsick's example, if terrain is at 3500 (and particularly if height would enhance the chance to glide to a good outlanding area) I would have no hesitation in using that as the reason to go above 5000, still using the odds & evens + 500 principal.

 

 

 

4 There was another discussion on these forums about the 5000 ft "limit" and with the increase in performance of RAA aircraft, it is probably a tad outdated ........ but as I understand it, all you need is a good reason to go above it.

 

 

 

However Mick's article brought it home to me that with the tendency with a GPS to use data base airports as waypoints, many from down south might be using say West Wyalong or Temora or Narranderah or Forbes as waypoints or for fuel and therefore agglomerating (hopefully not literally) to an excessive degree, or more than the pilots may realise, well before Narromine. (Sorry if this makes airsick's point again as per post #4).

 

 

 

On the other hand, tell one of your mates that you'll meet up with them overhead a nominated waypoint and it's usually pretty hard to find them.

 

 

 

Regards Geoff

 

 

[slartibartfast]

Exactly Geoff.

 

I was off finding the link before I posted pretty much the same.

 

VFR (or hemispherical) cruising levels should be adhered to, even below 5000' or we get the anarchy previously described.

 

The relevant bit on the RAA site about airspace regulations is here.

 

If the terrain is 3,000 - 4,000 feet, or there is a dearth of landing options, you have every right to cruise at 5,500 (or 7,500 or even 9,500) if going east (even if west), and probably should.

 

Flying above 5,000' where still in class G is at the pilots discretion. Safety is the main factor.

 

I agree that sticking to the right of track is a good idea, as is not flying too straight on the GPS track between common waypoints.

 

Cheers,

 

Ross

 

 

[Guest Crezzi]

If you guys can fly that accurately you should either join the Roulettes or spend less time watching the GPS

 

I've done a lot of xc with other planes and when we both independently navigated (even with gps) we were usually on just close enough to see each other !

 

Cheers

 

John

 

 

[Mazda]

People in aviation reform have been trying to introduce offset tracking for many years for exactly this reason. The plan from way back in the 1990s was for aircraft (on IFR two way routes particulary) to track something like 0.2 miles to the right of track. I think there was even an AIP sup out on it at one time.

 

The only reason it was never really accepted was because some airline pilots thought that "professional" pilots should be bang on track, flying right in the centre of the airway. There was enough resistance to stop it being universally accepted.

 

It's not quite such an issue when flying VFR from random airports to other random airports in VMC when you can see out of the window!

 

 

[Guest airsick]

It's not quite such an issue when flying VFR from random airports to other random airports in VMC when you can see out of the window!

Part of my concern is that people are moving more 'into' the cockpit and watching the GPS too much. Even if they aren't too far into the cockpit if they rely on the GPS then they are more likely to be ontrack than they otherwise would be. As discussed elsewhere, closing speeds become an issue even if you do see oncoming traffic. I like the idea of implementing some sort of rule or convention of tracking to the right or left of the designated track until a few miles out. Even with the prescribed levels this wouldn't go astray.

 

Maybe we should start a movement! Bugger the airline pilots, I want to be safe more than I want a big ego.

 

 

[Captain]

Part of my concern is that people are moving more 'into' the cockpit and watching the GPS too much.

I disagree airsick.

 

 

 

An occasional squizz at the GPS is all it takes to stay on track, to know exactly where you are and to get a feel for winds.

 

 

 

I find that takes a lot less time "inside" the cockpit than it used to take to look down at the ground for landmarks, then look at my watch and note the times, then scribble it all on a pad, then check track and position vs planned course, then mark it on the charts and determine drift and + or - on the schedule, like we are all taught to do when X-Country.

 

 

 

Used well, I reckon a good GPS (particularly a moving map), together with a radio, are great tools for accurate and safe aviation with good situational awareness when X-country, and I believe that they actually increase the time available to sit back and use your peepers for good visual scans.

 

 

[Guest airsick]

I agree with you Captain, GPS is a great tool but only when used properly. As long as people are not keeping their eyes on the GPS and are looking outside then it is an aid. My concern, not sure if it is really happening, is that people are not doing this.

 

I recall reading an article some time ago that people are becoming worse drivers due to safety enhancements in modern cars. The argument was that someone who has an old car will drive to their ability. Give them a car with say ABS and all of a sudden they feel that their abilities have increased and they drive a bit harder or faster.

 

Does GPS do this? Does it mean that people feel they have to be less attentive to what is going on around them in the outside world? I'd like to think not but can't help but wonder. For the IFR guys these things are a huge help, their eyes are inside anyway and separation is done elsewhere, but for us VFR I am not so sure. Looking inside too much, I stress too, is not a good thing.

 

 

[Vorticity]

I think GPS is a great tool but must be applied with thought as to how you are operating. Not so much different to all flight planning, I know I dont do any serious planning if I am flying a 20 min leg that I regulary do, and yet some have told me I am crazy for this. Since I fly around at 50kts in a 2 stroke engine I am mainly concerned with flying map to ground (since I have time) and choosing the best outlanding fields. To simply follow an imaginary line accross the earth could lead to trouble for me, given what I am flying. The strange bit is that the 1 time I have been really scared during a Nav was using a GPS, I misread the information things where happening fast (obviously not in the drifter this day!) and I started making decisions based on some pixels rather than sticking my head out the window and having a look around.

 

 

[Ultralights]

just another related question, when planning a trip and drawing tracks on the map, do people still plan to navigate via well known or spotted landmarks or aids? or simply select a altitude and fly direct from point A to B, in regards to airspace restrictions etc???

 

even though i have a hand held GPS, i still plan to fly via VOR stations or major roads/rail lines and other forced landing safe terrain, and plot the waypoint into my GPS as well.

 

i think the only negative to GPS navigation as a primary means is the tendency for people to fly point a to b direct and resulting track taking them over tiger country or other terrain not really good for a forced landing.

 

 

[Yenn]

GPS should be the backup, not the primary navigation tool. It can and no doubt will go down or the machine may fail. Nothing works forever.

 

My method is to fly by map reading and use the GPS to keep an eye on where I am. It is great to be able to say you are 9.2 miles SE of Gundaroo at whatever height. That way the other pilots have a good idea of where you really are.

 

 

[Guest Andys@coffs]

Autopilot

 

There are now quite a number of us that have 2 or 3 axis autopilots fitted that tie directly to the NMEA output from the GPS. While some will argue that to fly an accurate track by hand, GPS on or off can be difficult, an Autopilot has the ability to fly the track exactly + or - a hundred feet either side and to within +-20ft in altitude

 

In fact the Autopilot that I have fitted (Trio Avionics) has the ability to program a track offset for exactly that reason and it mentions the risk of mid air collision as the reason for using this capability in the users manual.

 

Now in reality I guess if I was flying from greater Melb to Narromine, or greater syd to Narromine then the risk is higher, however in flying Adelaide to narromine across the GAFA I still guess that the 1st aircraft I would see would be between 3-5nm from Narromine;)

 

However.....<sigh!> An unfinished pergola means Narromine is a memory from last year, and something to be reconsidered next year:sad:

 

Andy

 

 

[Guest brentc]

It is a recommendation in AIP's to navigate to the right of the GPS track. Can't remember the exact distance reference. That way you double the distance from the guy going the other way if he's at your height.

 

 

[facthunter]

Height.

 

I'd like to think that he wouldn't be at your height, But that's another story. Vertical separation is a good idea that has a bit of potential for improvement. N..

 

 

[Guest airsick]

It is a recommendation in AIP's to navigate to the right of the GPS track. Can't remember the exact distance reference.

Can you remember where in the AIP's? I haven't heard this before and glanced through them earlier but found nothing.

 

 

[markendee]

Isn't this a hot bed?

 

I really do not want to argue as it never changes anyone's mind. No one wins.

 

All I will say is this, my whole nav ex's were based on forecast winds (winds at height based on who knows what?)

 

Flying by GPS is relative to actual conditions.

 

Mark

 

 

[motzartmerv]

Where is it said that below 5000 ft we don't adhere to atmospheric cruise levels..the sticker in our jab goes from 500 ft odds and evens for vfr..Whats the problem??

 

I think there are to many variables at play to put 2 gps aircraft on perfect recioricle headings and heights, and if cruise levels are obeyed then theres no problem, only during climb and descent..

 

As to the eyes in the cockpit thing, i always fly the arrow and pick a point way out on the horizen, a hill, a lake, anything that won't move and fly towards that, or fly the heading rather then the arrow..And i also use maps and mark my position evry 10 miles in case the yanks turn the lights out..

 

my 2 cents

 

 

[vk3auu]

First of all, it is 5000 feet above mean sea level.

 

I always program the waypoints into the GPS to give me another guide to where the track is. That track is necessarily designed to avoid CTA and inhospitable terrain. Then I fly with reference to the ground so as to avoid tiger country as much as possible, with the relevant map sitting on my lap in case the GPS dies. I may get a fair bit off the GPS track if I am in unfamiliar territory, but that doesn't happen too often these days. When I can, I get about half a mile to the right of the direct track. The GPS is mainly used to tell me how far or how long it is to the next waypoint. That gives me a double check on how much fuel I have left, as often, the forecast winds can be a bit different to actual.

 

David

 

 

[motzartmerv]

yep, sorry, thats right..It is amsl.., but the handbook says,

 

(a) the aeroplane may be flown 5000 feet above mean sea level or higher:

 

(1) only if it is flying over an area of land or water the condition and location of which is such that during the flight the aeroplane would be unable to land with a reasonable expectation of avoiding injury to persons onboard the aeroplane, and

 

(2) only if it is equipped with a radio communications device..

 

So from that we can take, if your flying over tiger country you can go over 5000 ft. with a radio of course..